In WW2, later US president John F. Kennedy and his crew disappeared after their torpedo boat had sunk. Can my readers help to make sense of an encrypted message that was sent a few days later?
As many of my readers already know, I’m currently co-writing a book about codebreaking with my US friend Elonka Dunin. This work is already announced on Amazon, publication is scheduled for November.
One of the topics Elonka and I address in our book is the Playfair cipher. As an example, we plan to cover a Playfair message that has a close relationship to John F. Kennedy.
Kennedy took part in the Second World War as a young naval officer. In 1943, he commanded a military boat, PT-109 …
…, which was crashed into by a Japanese destroyer. Kennedy and his crew washed up on the beach of a nearby island. Australian coastwatcher Sub-Lieutenant Reginald Evans, who had observed the crash, coordinated a successful rescue effort.
A Playfair message
During his coordination work, Evans sent and received multiple messages encrypted with the Playfair cipher. One of these messages is depicted in David Kahn’s book The Codebreakers.
The plaintext is noted below the message. It’s easy to read, and the ciphertext can be easily decrypted with the keyword ROYAL NEW ZEALAND NAVY.
The Playfair cipher used in this context follows the usual Playfair rules, except that doubled letters are not avoided by adding an X (e.g., OO becomes OXO before the substitution step), but are left unchanged (e.g, OO is encrypted to OO).
Another Playfair message
The National Cryptologic Museum has provided Elonka and me a few more ciphertexts of the same kind, also sent or received by Reginald Evans. As far as we know, these cryptograms have never been published in the crypto literature.
Here’s a Playfair message from August 7nd, 1943, five days after the crash:
Here’s a transcript of the ciphertext:
XELWA OHWUW YZMWI HOMNE OBTFW MSSPI AJLUO EAONG OOFCM FEXTT CWCFZ YIPTF EOBHM WEMOC SAWCZ SNYNW MGXEL HEZCU FNZYL NSBTB DANFK OPEWM SSHBK GCWFV EKMUE
The keyword used was PHYSICAL EXPERIMENTATION, which led to the following Playfair matrix:
PHYSI CALEX RMNTO BDFGK QUVWZ
Again, the plaintext is noted next to the Playfair message. It starts with: ELEVEN SURVIVORS PT BOAT …
However, this time the (alleged) plaintext is hard to read. Elonka and I tried to decipher the cryptogram (with CrypTool 2 and the Rumkin.com Cipher Tools) and to match the result with the purported plaintext, but only the first few letters made sense.
In addition, we wonder why there is a J in the ciphertext, although the Playfair cipher is usually based on a 25-letter alphabet without a J.
Can a reader tell us how this ciphertext can be decrypted and if it matches the plaintext noted on the same sheet?
Of course, we will include everybody who provides a helpful advice in our acknowledgement list, which is a part of the first book chapter.
Further reading: My steganographic gravestone tour (1): The grave of William and Elizebeth Friedman